[13] THE OSTEOLOGY OF AMIA CALVA. 759 



tached^ to the hinder extremity of the skull, as in the higher fishes which are 

 provided with ossified skulls. 



In Polypterus a free occipital arch has been described by Traquair. 

 Franque has also observed the occipital arches of Amia, as would ap- 

 pear from his brief and sot entirely lucid description, but their signifi- 

 cance appears to have entirely escaped him. Bridge mentions them 

 also. Here and there other authors have noticed them, without having, 

 up to the present time, placed any weight upon the occurrence of pre- 

 cisely the same thing in bony fishes. I have been able also to convince 

 myself that the occipital arch is not wanting in Leptidosteus. In this 

 Sauroid I find both halves synosteologically joined together, as well as 

 with the basioccipital, so that this latter bone appears to form by itself 

 the periphery of the occipital foramen. Among the osseous fishes one 

 finds in the pike free occipital arches beautifully developed, also in the 

 Salmonidae and Clupeidae ; but, as shall now be particularly mentioned, 

 proof can be furnished that all Teleostei originally possessed occipital 

 arches. 



Over the occipitale laterale, and connected with it at one small point, 

 is found the conical exoccipital (Plate I, Fig. 1, Ex.). It constitutes 

 the boundary to the entrance of the temporal fossa, mesiad, and is 

 partly covered on its superior surface by the posterior margin of the 

 parietal. 



The posterior lateral angle of the primoidal cranium is occupied by a 

 thoroughly developed bone, which I, in concurrence with Bridge, can 

 only take to be the intercalare (opisthotic) (Plate I, Figs. 1, 2, and 3, Jc.). 

 It is also a conical bone, which is covered above by the posterior lateral 

 angle of the squamosum, and which helps to form the lateral boundary 

 of the entrance to the temporal fossa. It does not articulate with the 

 exoccipital, but remains separated from it by a strip of cartilage lying 

 at the base of the temporal fossa. Posteriorly and beneath it comes 

 in contact with the occipitale laterale, and in some individuals also with 

 the basioccipital. Below and anteriorly, the intercalare, though a very 

 delicate process, meets and unites with a process from the petrosal. 

 To the apex of this bone, chiefly projecting posteriorly, the inferior limb 

 of the supraclavicular is attached, as already shown, by means of firm 

 ligaments. Below, the intercalare meets with the cartilage of the pri 

 moidal cranium, at which point something of aprotuberance is developed. 



It is known that in most osseous fishes the intercalare is wanting, 

 and in the minority, where it still exists, it is feebly developed, with 

 the exception of the family Gadidae.^^ 



Yet a comparison of the condition in Amia with that of the Gadidce 

 leaves not a shadow of a doubt that the bone just described is really 

 the intercalare, inasmuch as this very bone in the Gadidae possesses 



^Compare the careful description of the intercalare of the Gadidse by Vrolick, 

 " Studien iiier die Verhuodherung und die Knoohen des Schadels der Teleostei." Niederland. 

 Archiv. f. Zoologie, Bd. I, 1873. 



